The Stuff Of Legend...
Some entities in fantasy have stood the test of time. They are either so old or so powerful that they have outlasted every adventuring party that has sought their ruin, or already stand amongst the gods and devils that rule the multiverse. Ancient dragons, demon lords, aberrations that rule the Underdark...these and so many more fill the world of fantasy with legend.
Legendary Resistance / Legendary Actions
Many legendary creatures are tougher than your average beastie, and show that in their Legendary Resistances. Three times per long rest, if a creature with this feature fails a saving throw, they can choose to succeed instead. This pisses off my players to no end, but this is a great mechanical representation as to why these things have survived as long as they have. An ancient being wouldn't be able to be charmed by one unlucky roll out of the gate; it has some fortifications against that.
Conversely, legendary beings are often, but not always, solo endeavors. In other circumstances, such encounters can feel a little...one-sided. As a party of 5-7 warriors gang up on a single creature, that's usually 5-7 swings on it before it gets its turn.
Legendary ACTIONS provide a pseudo-set of extra turns each round for a Legendary Creature to use, simulating its great power and rebalancing the economy of the encounter.
At the close of another creature's turn, not its own, this creature can spend 1-3 Legendary Actions to perform certain tasks, attacks, or powers, as dictated by their stat block. Some powers burn only 1 LA, while others can burn 3 at once, especially if the creature is attempting something very powerful. Sometimes it's a movement or an extra attack, or a bonus spell. Whatever it is, stay alert! There's a reason these things are legendary.
But to be clear:
Legendary Resistances only recharge during a Long Rest, but...
Legendary Actions return at the start of the creature's turn EVERY ROUND.
So you might force some saves and use up their resistances...but they're just as dangerous with their Legendary Action economy.
A Creature's Lair
Location, location, location...
A Legendary being often has a place it calls its home. A "lair," if you will.
Such a place tends to grant them superior bonuses to their defenses, like a homefield advantage, and often pose great danger to an unprepared party.
A Lair in a Legendary encounter acts on an Initiative count (often count 20) like a character, but you can't attack it or defeat it. Maybe you're fighting in a volcano, and a wave of extreme heat hits you; or a pulse of necrosis randomly strikes someone within range of the dark altar of the Lich. And many effects get worse the longer the fight goes on, so entering a Lair with a clear strategy will help keep your party alive and (hopefully) end this encounter quickly in your favor.
Pro Tip: If ever you can engage a Legendary Creature outside of its Lair, do so. Those homefield advantages, coupled with its already frustrating extra actions and resistances, make these fights particularly nasty.
Other Special Traits
Powerful creatures, not just legendary ones, can often have extra special abilities to be aware of that set them apart from your average hobgoblin or bulette.
Some monsters have the ability to cast specific spells as part of their features. These spells, unless otherwise noted, are always cast at their lowest level. If it's a cantrip, we can assume the creature's challenge rating (CR) as its level if we need to determine damage (unless it's otherwise noted).
Innate spells often have other restrictions, like "target self" or "Reaction only."
A monster with the Spellcasting feature is considered to have a spellcasting level and an arsenal of spell slots, as if they were a player class. Such a creature can choose to cast spells at higher spell slots, just as a player might, giving a large bredth of caster flexibility (and making them very dangerous).
Psionics is a form of spellcasting that allows a monster to cast spells using only the power of its mind. This tag can be attached to both Innate and standard Spellcasting, and carries no additional rules, but other parts of the game might refer to it.
Assume, though, that a spell cast using Psionics does not require components. ;)
And there you have it!
Next time, we delve into the depths and visit one terrifying little beastie. I mean it, this thing's the stuff of nightmares!
See you at the table.
Professional Game Master musician, music teacher, game designer, and aspiring fiction author.